Iliotibial (IT) Band Syndrome: This condition is characterized by inflammation of the iliotibial band, a ligament that runs down the outside of the thigh from the hip to the knee. It is a common cause of lateral knee pain, especially in individuals who participate in activities that involve repetitive knee flexion and extension, such as cycling, running, or standing for long periods. The pain typically worsens with continued activity.

Lateral Meniscus Tear: A tear in the lateral meniscus, which is the cartilage structure in the knee joint, can cause lateral knee pain. This pain may be exacerbated by standing, twisting, or bending.
Lateral Collateral Ligament (LCL) Sprain: An injury to the LCL, which connects the femur (thigh bone) to the fibula (outer lower leg bone), can lead to lateral knee pain and instability.
Popliteus Tendinitis: Inflammation of the popliteus tendon, which helps to rotate the knee, can cause pain on the lateral side of the knee.

Osteonecrosis of the Femoral Condyle: A condition where the bone tissue of the femoral condyle (the end of the femur that forms part of the knee joint) dies due to lack of blood supply. It can cause severe knee pain and must be treated promptly to prevent further damage.
Tumor: Although rare, a tumor in the lateral aspect of the knee could cause pain, especially if it involves the bone or soft tissues.
Infection (Septic Arthritis or Osteomyelitis): Infections within the knee joint or bone can cause severe pain, redness, and swelling, and require immediate medical attention.

Peroneal Nerve Compression: Compression of the peroneal nerve, which runs down the lateral aspect of the knee, can cause pain, numbness, and weakness in the area it supplies.
Fabella Syndrome: A small, sesamoid bone called the fabella, located in the lateral aspect of the knee, can cause pain if it becomes inflamed or irritated.
Ganglion Cyst: A benign lump that can develop on the lateral side of the knee, potentially causing pain and discomfort.